The present invention relates to carburettors for internal combustion engines of the type comprising an acceleration pump whose variable-volume chamber is connected to a float chamber through an inlet passage and to the part of the induction passage of the carburettor situated upstream of an operator actuatable throttle member by a delivery passage with a delivery check valve, said variable volume chamber being defined by a movable wall mechanically connected to the throttle member and arranged for reducing the volume of the chamber upon opening movement of said throttle member.
The acceleration pump is for delivering liquid fuel to the induction passage during acceleration, i.e. during opening of the throttle member of the carburettor. But any action on the accelerator pedal causes delivery of fuel to the engine. While that delivery is useful when the engine is operating and must be accelerated, the fuel is not only wastefully consumed but further tends to "drown" the engine through an excess of richness if the throttle member is opened while the engine is stopped. This drawback is particularly noticeable on starting up an engine which is still hot: if the driver depresses the accelerator pedal several times in succession, the engine is drowned and can only be started up again after several minutes.
It is an object of the invention to provide a carburettor with an acceleration pump which is improved particularly in that the action of the acceleration pump is suppressed when not necessary.
According to the invention, a carburettor of the above-defined type has an acceleration pump which is disabled as long as the engine is stopped.
In a preferred embodiment, a connecting linkage between the throttle member and the movable wall of the acceleration pump is associated with a locking device which renders the pump inactive when the engine is at rest and which is subjected to the depression which prevails in the induction passage so as to allow the pump to operate when the depression is at a level indicating that the engine is running. The locking device may typically comprise a ball guided in a passage formed in the body of the carburettor, movable between a rest position in which it projects outside the body into a cavity or notch provided in a lever which actuates the pump so as to secure said lever against movement and a disabled position into which it is brought by said depression. The device may additionally include a manually or thermostatically controlled valve prohibiting, when closed, application of the depression to the locking device.
In another embodiment of the invention, the locking device may be arranged to prevent operation of the acceleration pump when the engine is stopped and to limit the amount of fuel fed by the acceleration pump to the engine during acceleration to a value which depends on the amount of depression in the induction passage.
According to yet another embodiment of the invention, operation of the pump when the engine is stopped is avoided by disabling the mechanical linkage from the throttle member when the engine is stopped.
The invention will be better understood from the following description of particular embodiments, given by way of examples. The description refers to the accompanying drawings.